If you are applying for a multiple-entry visa but have only planned your first visit, build the flight reservation around that real trip rather than inventing dates for journeys you have not arranged. Check the destination's current application checklist to see what it asks for; where it requests the first intended visit, a coherent first-trip itinerary is more useful than speculative flights for a future holiday.
Why the first trip needs to be clear
A multiple-entry visa can be intended for several visits over a period of time, but that does not mean every later trip is already booked. You may know that you want to visit Europe in May, return for a family wedding in September and perhaps attend a conference the following spring. At the time of the application, only the May trip may have fixed dates.
Your flight reservation should describe that May trip accurately. For example, you might plan to fly from Istanbul to Rome on 8 May and return from Rome to Istanbul on 16 May. Your hotel dates, leave dates and other travel documents should support the same period. There is no benefit in adding a made-up September flight merely to make the file appear more complete.
Some official checklists for multiple-entry applications explicitly refer to the reservation for the first visit, while others may ask for different evidence. The European Commission's published supporting-document list for applicants in Türkiye identifies flight reservations or other proof of intended transport, alongside accommodation evidence. Always use the current checklist for the specific country and application route rather than treating a sample checklist as a universal rule.